Stable isotope ratios in shells of marine organisms

Oxygen and carbon isotope analyses have been carried out on calcareous skeletons of important recent groups of organisms. Annual temperature ranges and distinct developmental stages can be reconstructed from single shells with the aid of the micro-sampling technique made possible by modern mass-spectrometers. This is in contrast to the results of earlier studies which used bulk sampIes. The skeletons analysed are from Bermuda, the Philippines, the Persian Gulf and the continental margin off Peru. In these environments, seasonal salinity ranges and thus annual variations in the isotopic composition of the water are small. In addition, environmental parameters are weIl documented in these areas. The recognition of seasonal isotopic variations is dependant on the type of calcification. Shells built up by carbonate deposition at the margin, such as molluscs, are suitable for isotopic studies. Analysis is more difficult where chambers are added at the margin of the shell but where older chambers are simultaneously covered by a thin veneer of carbonate e. g. in rotaliid foraminifera. Organisms such as calcareous algae or echinoderms that thicken existing calcareous parts as weIl as growing in length and breadth are the most difficult to analyse. All organisms analysed show temperature related oxygen-isotope fractionation. The most recent groups fractionate oxygen isotopes in accordance with established d18O temperature relationships (Tab. 18, Fig. 42). These groups are deep-sea foraminifera, planktonic foraminifera, serpulids, brachiopods, bryozoa, almost all molluscs, sea urchins, and fish (otoliths). A second group of organisms including the calcareous algae Padina, Acetabularia, and Penicillus, as weIl as barnacles, cause enrichment of the heavy isotope 18O. Finally, the calcareous algae Amphiroa, Cymopolia and Halimeda, the larger foraminifera, corals, starfish, and holothurians cause enrichment of the lighter isotope 16O. Organisms causing non-equilibrium fractionation also record seasonal temperature variations within their skeletons which are reflected in stable-oxygen-isotope patterns. With the exception of the green algae Halimeda and Penicillus, all organisms analysed show lower d13C values than calculated equilibrium values (Tab. 18, Fig. 42). Especially enriched with the lighter isotope 12C are animals such as hermatypic corals and larger foraminifera which exist in symbiosis with other organisms, but also ahermatypic corals, starfish, and holothurians. With increasing age of the organisms, seven different d13C trends were observed within the skeletons. 1) No d13C variations are observed in deep-sea foraminifera presumably due to relatively stable environmental conditions. 2) Lower d13C values occur in miliolid larger foraminifera and are possibly related to increased growth with increasing age of the foraminifera. 3) Higher values are found in planktonic foraminifera and rotaliid larger foraminifera and can be explained by a slowing down of growth with increasing age. 4) A sudden change to lower d13C values at a distinct shell size occurs in molluscs and is possibly caused by the first reproductive event. 5) A low-high-Iow cycle in calcareous algae is possibly caused by variations in the stage of calcification or growth. 6) A positive correlation between d18O and d13C values is found in some hermatypic corals, all ahermatypic corals, in the septa of Nautilus and in the otoliths of fish. In hermatypic corals from tropical areas, this correlation is the result of the inverse relationship between temperature and light caused by summer cloud cover; in other groups it is inferred to be due to metabolic processes. 7) A negative correlation between d18O and d13C values found in hermatypic corals from the subtropics is explained by the sympathetic relationship between temperature and light in these latitudes. These trends show that the carbon isotope fractionation is controlled by the biology of the respective carbonate producing organisms. Thus, the carbon isotope distribution can provide information on the symbiont-host relationship, on metabolic processes and calcification and growth stages during ontogenesis of calcareous marine organisms.

Physical properties, sedimentation rates, and accumulation rates of bottom sediments from the Laptev Sea collected during SPASIBA-91 Russian-French Program

Humidity and wet and dry bulk densities were determined for bottom sediments of the Lena River marginal filter within a 700 km section from the outer boundary of the river delta. Earlier determinations of suspended matter concentration in water, material and grain-size composition and age of sediments were made along the same section. Sediment matter fluxes (accumulation rates), their changes in space and time (about 14 ka) were inferred from measurements of physical parameters. A correlation was found between the physical parameters of bottom sediments and changes in the Lena river marginal filter including those caused by sea-level fluctuations.

Sulfur speciation in bottom sediments from deep-sea basins of the Atlantic Ocean

Distribution of reduced sulfur forms in vertical sediment sections in deep-sea basins of the Atlantic Ocean is under study. Presence of weak sulfate reduction process resulted from low concentrations of reactive organic matter and differing by characteristic features of the initial stage of development. Interpretation of results is given on the base of consideration of dynamic redox equilibrium in the system: reduced sulfur - dissolved oxygen.

Chemical composition of sediments from the Indian Ocean

Intensive reduction processes within bottom sediments from the Bay of Bengal lead to marked enrichment of the oxidized layer in iron and manganese. This is not observed in sediments from the Arabian Sea. Oxidized bottom sediments in central areas of the Indian Ocean show high iron concentrations, but fraction of reactive Fe in total Fe is lower. Manganese concentration increases steadily with distance from the shore to the pelagic region of the ocean, and fraction of reactive manganese also increases in the same direction. There is close correlation between total Mn and Mn(4+) in these sediments.

(Table, page 233) Comparative analysis of manganese nodules

A preliminary report on the manganese nodule field southwest of Western Australia published in this Journal recently (Frakes, Exon and Granath, 1977) quoted chemical analyses which were carried out on air-dried material. Significantly higher metal values have been recorded in some later analyses done on nodules dried at 105°C. Tests have shown that the ground, air-dried material retains considerable moisture, which accounts for the higher metal values of the later analyses. The average water content (after drying at 105°C) has been determined at 16 percent. The relevant chemical data now available on this material are summarised in the accompanying table: in this table metal values (by atomic absorption spectrophotometry) have been recalculated assuming a moisture content of 16 percent.

Data on multidisciplinary research in the Tajura Rift (Gulf of Aden) during Cruise 7 of R/V Akademik Mstislav Keldysh in winter 1983-1984

In the collective monograph results of geological and geophysical studies in the Tadjura Rift carried out by conventional outboard instruments and from deep/sea manned submersibles "Pisces" in winter 1983-1984 are reported. Main features of rift tectonics, geology, petrology, and geochemistry of basalts from the rift are under consideration. An emphasis is made on lithology, stratigraphy, and geochemistry of bottom sediments. Roles of terrigenous, edafogenic, biogenic, and hydrothermal components in formation of bottom sediments from the rift zone are shown.

137Cs in waters and bottom sediments of the Sea of Japan in 2002 and 1994

During an expedition aboard R/V Pavel Gordienko (September, 2002) investigations in the Sea of Japan areas, where radioactive wastes were disposed by the former Soviet Union, were carried out in order to assess present level of radioactive contamination of marine environment. Concentration of I37Cs, radioecologically one of the most important radionuclides, in near-bottom sea water and bottom sediments were measured to be low, 2.8-17.2 Bq/m**3 and 3.2-27.2 Bq/kg dry weight, respectively, that did not differ significantly from levels elsewhere in the northwest Pacific Ocean arising from global fallout. Results of measurements were compared with results of the Joint Japanese- Korean -Russian expedition to the Sea of Japan in 1994.

Physical properties of four profiles from the Triassic in Germany

The Norian Steinmergel-Keuper (SMK) represents a low-latitude cyclically-bedded playa system of the Mid-German Basin. We investigated a drilling site (core Morsleben) and sections from marginal positions. Dolomite/red mudstone beds form rhythmic alternations that were associated with varying monsoon activity. Hence, low K/Al ratios of dolomite beds suggest increased chemical weathering of the crystalline hinterland and therefore increased monsoonal rainfall. High K/Al ratios in red mudstone beds reflect increased physical weathering of the hinterlands during dryer periods. Dolomite layers reflect the lake stage (maximum monsoon) while red mudstones indicate the dry phase (minimum monsoon) of the playa cycle. We distinguished five major types of cyclic facies alternations, representing specific facies zones in the playa system. We have implemented spectrophotometry as a tool for high-resolution cyclostratigraphy. The dense sampling increment (up to 1 cm) allows for the recognition of all orbital frequencies. Sediment colour profiles reveal striking hierarchical cycles from semi-precession (SP, 99 kyr) over precession (P, 19.8 kyr) and obliquity (O, 36 kyr) to eccentricity (E1-2 109 kyr; E3, 413 kyr). A significant about 2 Myr-signal is attributed to the longer-term eccentricity E4. One monsoonal (precession) cycle includes two carbonate precipitation events. We propose that stratified mudstone and red mudstone are associated with maximum and minimum monsoon during the transition of the solstices in perihelion and aphelion, respectively. The two carbonate precipitation events were most likely created when equinoxes were in perihelion and aphelion, respectively. A sedimentary semi-precession response cycle is a novel finding for the Norian strata. The obliquity signal is attributed to incoming atmospheric moisture from the northeast of the SMK basin. The E4 cycle controls lake-level changes over long times. Apparently, E4 is responsible whether or not a threshold value is crossed. Bundles of 109 kyr and 413 kyr in red mudstones suggest a dry system with reduced monsoonal activity. In contrast, humid periods reveal thick layers of dolomite beds, indicating that during those intervals the monsoonal activity was strong enough to prevent the playa system from drying out completely.

Composition of sediments, hydrothermal manifestations, interstitial waters, and aeolian material from the TAG Hydrothermal Field and Central Atlantic

The book is devoted to regularities of spatial distribution, mineralogy and geochemistry of hydrothermal and hydrothermal-sedimentary manifestations of the Mid-Atlantic Ridge rift zone.

Age model, isotope analyses, geochemical measurements and grain size analyses of sediment core GeoB9508-5 from the Senegal River Mouth

The influence of the large-scale ocean circulation on Sahel rainfall is elusive because of the shortness of the observational record. We reconstructed the history of eolian and fluvial sedimentation on the continental slope off Senegal during the past 57,000 years. Our data show that abrupt onsets of arid conditions in the West African Sahel were linked to cold North Atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with Heinrich Stadials. Climate modeling suggests that this drying is induced by a southward shift of the West African monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric African Easterly Jet.

Composition of bottom sediments, rocks, and ores from the Tropical Atlantic

Geological features of some areas of the Tropical Atlantic (stratigraphy, tectonic structure, lithology, distribution of ore components in bottom sediments, petrography of bedrocks, etc.) are under consideration in the book. Regularities of concentration of trace elements in iron-manganese nodules, features of these nodules in bottom sediments, distribution of phosphorite nodules and other phosphorites have been studied. Much attention is paid to rocks of the ocean crust. A wide range of mineralization represented by magnetite, chromite, chalcopyrite, pyrite, pentlandite, and other minerals has been found.

Concentrations of phosphates and silicon in near-bottom and interstitial waters of the Baltic Sea

Fine structure of vertical distributions of phosphorus and silicon in near-bottom layers and interstitial waters is studied in different regions of the Baltic Sea (Gulf of Finland, Bornholm area, Gotland trench). Data obtained are used to calculate fluxes of mineral forms of phosphorus and silicon in exchange processes between sediments and the near-bottom water layer. Depending on sediment types, values of nutrient fluxes vary from 9.8 to 632.6 µg-at/m**2/day for phosphorus and from 232.4 to 1881.1 µg-at/m**2/day for silicon. Fluxes calculated for different regions are compared.

Uranium and radioactive isotopes in bottom sediments and Fe-Mn nodules and crusts of seas and oceans

The main stages of the sedimentary cycle of uranium in modern marine basins are under consideration in the book. Annually about 18 thousand tons of dissolved and suspended uranium enters the ocean with river runoff. Depending on a type of a marine basin uranium accumulated either in sediments of deep-sea basins, or in sediments of continental shelves and slopes. In the surface layer of marine sediments hydrogenic uranium is predominantly bound with organic matter, and in ocean sediments also with iron, manganese and phosphorus. In diagenetic processes there occurs partial redistribution of uranium in sediments, as well as its concentration in iron-manganese, phosphate and carbonate nodules and biogenic phosphate detritus. Concentration of uranium in marine sediments of various types depending on their composition, as well as on forms of its entering, degree of differentiation and of sedimentation rates, on hydrochemical regime and water circulation, and on intensity of diagenetic processes.